1. Field
The present disclosure relates to a water splitting oxygen evolving catalyst, a method of preparing the catalyst, an electrode having the catalyst, and a water splitting oxygen evolving device having the electrode.
2. Description of the Related Art
Recently, hydrogen-based energy has been considered as a solution to address the exhaustion of carbon-based energy and environmental problems caused by fossil fuel emissions. Accordingly, efforts continue on methods to produce hydrogen by splitting water using the energy of the sun.
In order to split water, an improved photocatalyst, which produces electrons and holes by absorbing solar energy to make hydrogen and oxygen, would be desirable. However, since splitting water with high efficiency is difficult with only the photocatalyst, a co-catalyst (an electrocatalyst) has been proposed for hydrogen and oxygen generation. Particularly, a reaction rate of the oxygen generation reaction is slow since one oxygen atom is generated from 2 water molecules to yield 4 electrons (i.e., 2H2O→4H++4e−+O2). Thus, holes having an over voltage are desirable in order to increase the rate of the oxygen generation, but when the holes produced by the photocatalyst do not have enough over voltage, the oxygen generation rate may be insufficient. Therefore, the electrocatalyst is desired to improve oxygen generation.
Water splitting oxygen evolving catalysts known to date may be roughly divided into organic-based catalysts and inorganic-based catalysts. The organic-based catalysts may be decomposed by light, and thus, and thus have unsuitable stability. The inorganic-based catalysts may be subdivided into heterogeneous bulk oxide-based catalysts and homogeneous polyoxometalate-based catalysts (See, for example, Qiushi Yin et al., A Fast Soluble Carbon-Free Molecular Water Oxidation Catalyst Based on Abundant Metals, Science Vol. 328, 342 (2010)). The heterogeneous bulk oxides-based catalysts can have insufficient catalytic activity. Also, since the homogeneous polyoxometalate-based catalysts are uniformly dissolved in an electrolyte, a significant fraction of thereof is disconnected from an electrode, and thus, utility per unit weight is poor.
An oxygen-evolving electrocatalyst using cobalt (cobalt-oxide-phosphate, “CoPi”) has been recently developed by a group under professor Nocera at MIT (Matthew W. Kanan and Daniel G. Nocera, In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+, Science Vol. 321, 1072 (2008)), and although it is a heterogenous catalyst, it may be coated on an electrode in the amorphous state. Thus, a large amount of cobalt ions exposed in water or other solution is obtained, and thus, the catalyst has high catalytic activity.